1. Field of the Invention
Illustrative embodiments described in this patent specification generally relate to a drive transmission device and an image forming apparatus including the drive transmission device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, printers, facsimile machines, and multifunction devices having two or more of copying, printing, and facsimile functions, typically form a toner image on a recording medium (e.g., a sheet of paper) according to image data using an electrophotographic method. In such a method, for example, a charger charges a surface of an image carrier (e.g., a photoconductor); an irradiating device emits a light beam onto the charged surface of the photoconductor to form an electrostatic latent image on the photoconductor according to the image data; a developing device develops the electrostatic latent image with a developer (e.g., toner) to form a toner image on the photoconductor; a transfer device transfers the toner image formed on the photoconductor onto a sheet; and a fixing device applies heat and pressure to the sheet bearing the toner image to fix the toner image onto the sheet. The sheet bearing the fixed toner image is then discharged from the image forming apparatus by a sheet discharger.
The image forming apparatuses are often equipped with a detachably attachable process unit that contains multiple rotary bodies such as the photoconductor and a developing roller. The image forming apparatuses further include a drive transmission device that transmits a driving force from a drive source such as a motor to the photoconductor in the process unit. The drive transmission device is disposed within a housing of the image forming apparatus, and generally includes a motor gear attached to a shaft of the motor, a gear that engages the motor gear, and a coupling attached to a leading end of a rotary shaft to which the gear is fixed to engage an engaged part of the photoconductor.
However, with such a configuration, eccentric error upon attachment of the gear or the coupling to the rotary shaft may vary rotary speed of the photoconductor. In addition, in a case in which the driving force of the motor is transmitted to both of the photoconductor and the developing roller in the process unit via the gear, any load fluctuation on the developing roller is transmitted to the photoconductor. Consequently, the driving force is momentarily not transmitted from the motor gear to the gear due to backlash between the gear and the motor gear, possibly causing rotary speed of the photoconductor to fluctuate.
To counteract this problem, one known drive transmission device includes a photoconductor gear serving as a drive transmission member and having a gear part that engages a motor gear, a rotary shaft, and a coupling that engages an engaged part of a photoconductor. The gear part, the rotary shaft, and the coupling are formed together as an integrated unit, that is, the photoconductor gear, by pouring a resin into a mold using injection molding, thereby preventing eccentric error upon attachment of the gear part or the coupling to the rotary shaft. As a result, variation in rotary speed of the photoconductor can be prevented.
Further, in the above-described related-art drive transmission device, the motor gear fixed to a shaft of a motor engages both of the photoconductor gear and one of multiple gears that transmit a driving force from the motor to a developing roller. Accordingly, transmission of the driving force from the motor to the photoconductor is separated from transmission of the driving force from the motor to the developing roller. As a result, load fluctuation on the developing roller is transmitted to the motor gear through a gear train including the multiple gears that transmit the driving force to the developing roller. Because it is attached to the shaft of the motor and directly receives the driving force from the motor, the motor gear remains rotated by the driving force from the motor even when the load fluctuation in the developing roller is transmitted to the motor gear. Thus, the driving force is reliably transmitted to the photoconductor gear that engages the motor gear, thereby preventing variation in rotary speed of the photoconductor.
However, because the photoconductor gear and the multiple gears in the gear train are rotatably attached to a lateral plate of an image forming apparatus including the above-described drive transmission device, production costs of the lateral plate and installation cost are increased. Further, a size of the drive transmission device is increased, as described in detail below.
In order to reliably and evenly transmit the driving force of the motor to the photoconductor, it is important to accurately engage the photoconductor gear and the motor gear. Similarly, it is important to accurately engage the multiple gears in the gear train with one another in order to reliably and evenly transmit the driving force from the motor to the developing roller.
A mount on the lateral plate of the image forming apparatus to which the photoconductor gear is attached must be accurately formed to accurately attach the photoconductor gear to the mount, thereby enhancing accuracy in engagement of the photoconductor gear and the motor gear. In addition, multiple mounts on the lateral plate of the image forming apparatus to which the multiple gears in the gear train are respectively attached must be accurately formed to accurately attach the multiple gears to the respective mounts, thereby enhancing accuracy in engagement of the multiple gears. Further, a mount on the lateral plate of the image forming apparatus to which the motor is attached must be accurately formed to accurately attach the motor to the mount.
Therefore, in the above-described drive transmission device, higher production costs are needed for the lateral plate of the image forming apparatus to accurately form the mounts on the lateral plate. In addition, the photoconductor gear, the multiple gears in the gear train, and the motor must be accurately attached to the lateral plate, causing an increase in installation costs.
Further, because the multiple gears in the gear train are attached to the lateral plate of the image forming apparatus, it is necessary to dispose the gear train around the gear part of the photoconductor gear, thereby increasing the size of the drive transmission device.